Extraordinary Thermoelectric Properties of Topological Surface States in Quantum-Confined Cd 3 As 2 Thin Films.

Topological insulators and semimetals have been shown to possess intriguing thermoelectric properties promising for energy harvesting and cooling applications. However, thermoelectric transport associated with the Fermi arc topological surface states on topological Dirac semimetals remains less explored. In this work, we systematically examine thermoelectric transport in a series of topological Dirac semimetal Cd 3 As 2 thin films grown by molecular beam epitaxy. Surprisingly, we find significantly enhanced Seebeck effect and anomalous Nernst effect at cryogenic temperatures when the Cd 3 As 2 layer is thin. In particular, we observe a peak Seebeck coefficient of nearly 500 µV K -1 and a corresponding thermoelectric power factor over 30 mW K -2  m -1 at 5 K in a 25-nm-thick sample. Combining angle-dependent quantum oscillation analysis, magnetothermoelectric measurement, transport modeling and first-principles simulation, we isolate the contributions from bulk and surface conducting channels and attribute the unusual thermoelectric properties to the topological surface states. Our analysis showcases the rich thermoelectric transport physics in quantum-confined topological Dirac semimetal thin films and suggests new routes to achieving high thermoelectric performance at cryogenic temperatures. This article is protected by copyright. All rights reserved.